A light emitting diode (LED) is a device which converts an electrical signal into light using characteristics of a semiconductor. Since the development of an LED emitting red light in 1962, LEDs emitting various colors of light from infrared rays to visible and ultraviolet rays depending on used materials have been developed. In particular, a vertical-type LED safely emits light with low cost and thus is utilized in a wide range of applications.
Generally, an LED has a conversion efficiency of 40% or higher, and the remaining energy thereof is converted into heat energy. Thus, to solve a heat radiation problem of an LED, an LED with a vertical electrode structure is widely used. KR Patent Registration No. 10-0705225 discloses a method of manufacturing a vertical-type light emitting device. The vertical-type light emitting device is formed by sequentially stacking a light emitting structure and a pair of electrodes. However, a p-electrode used as a reflective electrode has a flat surface to reflect light mostly in the vertical direction, and thus a radiation angle is narrow.
Meanwhile, KR Patent Publication No. 10-2010-0095134 discloses a light emitting device formed in which a transparent electrode layer is formed on a conductive semiconductor layer. A transparent electrode using indium tin oxide (ITO) has excellent current spreading and thus is frequently used as an electrode. However, although an ITO thin film properly transmits infrared and visible light, the ITO thin film absorbs emitted ultraviolet rays with a short wavelength and thus has low transmission of ultraviolet rays emitted from a light emitting diode.
Accordingly, it is needed to develop a high-efficiency vertical-type LED which is capable of dispersing a radiation angle of light horizontally to widen the radiation angle and to increase light extraction efficiency. Also, it is needed to develop a high-efficiency ultraviolet LED emitting ultraviolet rays which does not reduce light output of emitted ultraviolet rays and is capable of achieving a certain level or higher of light properties, while using a traditional electrode material, such as a transparent electrode of ITO or metal electrode.